Phase-change materials, or "PCMs" are compositions that absorb and emit large amounts of heat by changing from one physical state to another, most often reversibly. Typical PCMs change from solid to liquid and back. Paraffinic hydrocarbons are commonly used as PCMs that melt at a desired temperature or over a desired temperature range, as disclosed, for example, in U.S. Pat. No. 5,637,389.
Phase-change materials find use or have been proposed for use in apparel for thermal management, either as discrete layers (see U.S. Pat. No. 5,499,460), as foam additives (see U.S. Pat. No. 5,637,389), as fabric coatings (see U.S. Pat. No. 5,366,801), and as additives to fibers (see U.S. Pat. No. 4,756,958). Where not used as discrete layers, PCMs may be encapsulated to minimize loss of their integrity, dissipation, or evaporation. Encapsulated PCMs are available as microcapsules ("MicroPCMs") having average diameters typically in the range of a few to a few hundred microns. MicroPCMs have been prepared for use as additives to heat exchange fluids, including motor oil (see U.S. Pat. No. 5,141,079).
PCMs which contain paraffinic hydrocarbons are typically flammable. This flammability is often an unacceptable condition. In the past, these difficulties have been overcome by either avoiding problematic physical environments, or by modification of the environments. This approach severely limits the applicability of MicroPCMs in many desirable applications. One approach to this particular problem is found in U.S. Pat. No. 5,435,376, which describes MicroPCMs which include flame resistant halogenated paraffins.
Sol-gel methods are generally covered in Sol-Gel Science--The Physics and Chemistry of Sol-Gel Processing, C. Jeffrey Brinker & George W. Scherer, 1st Ed., Academic Press, (1990), which is hereby incorporated by reference in its entirety.